A Dual-Band SiGe HBT Frequency-Tunable and Phase-Shifting Differential Amplifier Employing Varactor-Loaded, Stacked LC Resonators

A dual-band SiGe HBT frequency-tunable and phase-shifting differential amplifier has been developed for the future active phased array antennas with a multiband, multibeam, and multitarget tracking operation. The amplifier uses varactor-loaded, stacked LC resonators in the design of the output circuit in order to provide frequency-tunable and phase-shifting capabilities for dual frequencies. By utilizing the varactor-loaded LC resonator, which has a variable resonant frequency and a large insertion phase variation, frequency-tunable and phase-shifting performances become available. Moreover, by using the stacked configuration, the frequency and insertion phase can be varied independently for dual frequencies. A dual-band SiGe HBT differential amplifier has achieved a lower-frequency tuning range of 0.56 to 0.7？GHz for a higher fixed frequency of 0.97？GHz as well as a higher-frequency tuning range of 0.92 to 1.01？GHz for a lower fixed frequency of 0.63？GHz. A lower-frequency phase variation of 99° and a higher-frequency phase variation of 90.3° have been accomplished at 0.63 and 0.97？GHz, respectively. This is the first report on the dual-band differential amplifier with frequency-tunable and phase-shifting capabilities. 1. Introduction Recent and future wireless systems require a wide range of data rates over several frequency bands, and thus adaptive and reconfigurable transceivers become necessary to support high performance and flexibility [1]. Meanwhile, microwave and millimeter-wave sensors and radar systems require multiband, multibeam scanning phased array antennas as well as a multi-target tracking capability [2]. To address these requirements, multifunction capabilities are strongly required. Especially multiband amplification, frequency tunability, gain and phase control are crucial for realizing adaptive and reconfigurable phased array systems. Most of the traditional multiband amplifiers, however, provide a single function [3]. Meanwhile, the authors have presented multiband amplifiers with frequency-tunable as well as gain control capabilities for bandpass and bandstop types [4, 5]. To enhance the operational capability, a novel design approach is proposed in this paper for the multiband low-noise differential amplifier with frequency-tunable and phase-shifting capabilities. In order to realize both frequency-tunable and phase-shifting performances, varactor-loaded LC resonators are used in the design of the output circuit of the differential amplifier. LC resonators are widely used in the reflection type phase shifter because they provide